Question

I’m trying to grasp test driven development, and I’m wondering if those unit tests is fine. I have a interface which looks like this:

public interface IEntryRepository {     IEnumerable<Entry> FetchAll();     Entry Fetch(int id);     void Add(Entry entry);     void Delete(Entry entry); } 

And then this class which implements that interface:

public class EntryRepository : IEntryRepository {     public List<Entry> Entries {get; set; }      public EntryRepository()     {         Entries = new List<Entry>();     }      public IEnumerable<Entry> FetchAll()     {         throw new NotImplementedException();     }      public Entry Fetch(int id)     {         return Entries.SingleOrDefault(e => e.ID == id);     }      public void Add(Entry entry)     {         Entries.Add(entry);     }      public void Delete(Entry entry)     {         Entries.Remove(entry);     } } 

Theese are the unit tests I have written so far, are they fine or should I do something different? Should i be mocking the EntryRepository?

[TestClass] public class EntryRepositoryTests {     private EntryRepository rep;      public EntryRepositoryTests()     {         rep = new EntryRepository();     }      [TestMethod]     public void TestAddEntry()     {         Entry e = new Entry { ID = 1, Date = DateTime.Now, Task = 'Testing' };         rep.Add(e);          Assert.AreEqual(1, rep.Entries.Count, 'Add entry failed');     }      [TestMethod]     public void TestRemoveEntry()     {         Entry e = new Entry { ID = 1, Date = DateTime.Now, Task = 'Testing' };         rep.Add(e);          rep.Delete(e);         Assert.AreEqual(null, rep.Entries.SingleOrDefault(i => i.ID == 1), 'Delete entry failed');     }      [TestMethod]     public void TestFetchEntry()     {         Entry e = new Entry { ID = 2, Date = DateTime.Now, Task = 'Testing' };         rep.Add(e);          Assert.AreEqual(2, rep.Fetch(2).ID, 'Fetch entry failed');     } } 

Thanks!

Answer 1

Just off the top of my head…

Although your testing of add really only tests the framework:

• You’ve got adding 1 item, that’s good
• what about adding LOTS of items (I mean, ridiculous amounts – for what value of n entries does the container add fail?)
• what about adding no items? (null entry)
• if you add items to the list, are they in a particular order? should they be?

likewise with your fetch:

• what happens in your fetch(x) if x > rep.Count ?
• what happens if x < 0?
• what happens if the rep is empty?
• does x match performance requirements (what’s it’s algorithmic complexity? is it within range when there’s just one entry and when there’s a ridiculously large amount of entries?

There’s a good checklist in the book Pragmatic Unit Testing (good book, highly recommended)

• Are the results right?
• Are all the boundary conditions CORRECT
  • Conform to an expected format
  • Ordered correctly
  • In a reasonable range
  • Does it Reference any external dependencies
  • Is the Cardinality correct? (right number of values)
  • does it complete in the correct amount of Time (real or relative)
• Can you check inverse relationships
• Can you cross check the results with another proven method
• Can you force error conditions
• Are performance characteristics within bounds